Measurements and/or estimates of ambient pressure may be used as inputs in various vehicle control strategies in order to control engine operation. In one example, engines may include a dedicated, standalone barometric pressure sensor positioned in an intake passage of the engine (e.g., at or around an intake air filter) to measure ambient (or barometric) pressure. However, dedicated ambient pressure sensors may increase engine system costs and engine system control complexity. Some engine powertrain configurations may not include an ambient pressure sensor. Therein, the ambient pressure may be modeled based on engine operating conditions and/or other sensor measurements. However, the inventors herein have recognized that these ambient pressure models may have errors that may cascade into additional models that use the modeled ambient pressure as an input. Additionally, certain models may be bounded by a window in which ambient pressure may only be modeled under selected engine operating conditions. As a result, engine control based on ambient pressure estimates during operation outside of the window may have reduced accuracy.
In one example, the issues described above may be addressed by a method for: when propelling a hybrid vehicle using engine torque, estimating an exhaust air-fuel ratio via an exhaust oxygen sensor, and when propelling the vehicle using motor torque, estimating an ambient pressure of intake air via the exhaust oxygen sensor. In this way, an existing engine sensor (e.g., an exhaust oxygen sensor or an intake oxygen sensor) may be used to more accurately estimate engine ambient pressures, thereby increasing an accuracy of engine control based on ambient pressure estimates.
As one example, an exhaust gas sensor (e.g., exhaust oxygen sensor) may be positioned in an exhaust passage of an engine and operated to provide indications of various exhaust gas constituents. The engine may be coupled in a hybrid electric vehicle. During conditions when the engine is operating fueled, such as when the vehicle is propelled via engine torque, the exhaust gas sensor may be operated as an oxygen sensor at a reference voltage for enabling air-fuel ratio control. Additionally, the sensor may be operated as a variable voltage (VVs) oxygen sensor for estimating ambient humidity during conditions when the engine is operating non-fueled. When operating in the VVs mode, a reference voltage of the exhaust gas sensor is increased from a lower, base voltage (e.g., approximately 450 my) to a higher, target voltage (e.g., in a range of 900-1100 mV). In some examples, the higher, target voltage may be a voltage at which water molecules are partially or fully dissociated at the oxygen sensor while the base voltage is a voltage at which water molecules are not dissociated at the sensor. The inventors herein have further recognized that exhaust gas sensors have a characteristic pressure dependency. Since pressure changes the ability for oxygen to pass through the sensor's diffusion barrier, ambient pressure changes may be reflected in the sensor's pumping current output. Thus, during conditions when the engine is not being fueled, such as during an engine pull-down, or during a deceleration fuel shut-off event, the exposure of the exhaust gas sensor to ambient air at ambient pressure can be leveraged for ambient pressure estimation. In particular, when there is no engine fueling or combustion, the intake air in the intake passage of the engine is representative of ambient air. Therefore, the pressure of the intake air during those conditions is representative of an ambient pressure. During such conditions, an oxygen sensor can be used as a pressure sensor. Therein, an output of the oxygen sensor while operating at the lower reference voltage may be corrected based on an ambient humidity estimate. Then, based on an offset between the corrected oxygen sensor pumping current relative to a reference pumping current, and further based on a pressure dependency of the sensor, the ambient pressure may be determined. The pressure dependency of the sensor may have been previously characterized based on the sensor's response to varied pressure in ambient air. As an example, the ambient pressure may be characterized in response to a change in elevation of the vehicle as measured by an altimeter sensor. When fueled engine operation is resumed, engine operating parameters may be adjusted by a controller based on the determined ambient pressure estimate.
In this way, the need for a dedicated ambient pressure sensor is reduced, providing cost benefits over use of a standalone pressure sensor. In addition, a more accurate approach for estimating ambient pressure is provided in case of degradation of an existing ambient pressure sensor. As such, this allows the pressure information from the oxygen sensor to be used to tune powertrain performance instead of relying on potentially inaccurate inference from models. The technical effect of relying on an existing oxygen sensor for air-fuel ratio control during conditions when the engine is operating fueled, while using the same sensor for ambient pressure and humidity estimation during conditions when the engine is operating unfueled is that a new source for ambient pressure measurement is provided using pre-existing hardware. By relying on the pressure dependence of the oxygen sensor, pressure information from the oxygen sensor can be used to confirm the accuracy of other pressure sources (e.g., existing pressure sensors).
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.